1. Field of the Invention
The present invention relates to an apparatus and a method for cleaning substrates such as glass or disk-substrates, and particularly for cleaning semiconductor wafers.
2. Description of the Related Art
FIG. 5 shows a schematic sectional view of a conventional apparatus for cleaning semiconductor wafers. In the drawing, an ice maker 1 for producing frozen micro-particles 4 is supplied with a refrigerant such as liquid nitrogen, and is connected with a spray nozzle 3 which sprays ultrapure water. The ice maker 1 is covered with a thermal insulator (not shown). In a cleaning chamber 10 where a semiconductor wafer or the like is cleaned, a semiconductor wafer 7 is held by a semiconductor-wafer holding arm 6. The semiconductor wafer 7 held by the arm 6 can be moved by a conveying means 8. The frozen micro-particles produced in the ice maker 1 are ejected as the semiconductor wafer 7 by an injection nozzle 5 which is provided inside the cleaning chamber 10. Driving means 13 for controlling the positions and angles of the injection nozzle 5 is also provided inside the cleaning chamber 10. An exhaust blower 9 for exhausting the chamber 10 is provided at a bottom portion of the chamber 10.
In the conventional apparatus constructed as above, the inside of the ice maker 1 is chilled by evaporation of liquid nitrogen 2 supplied therein. After it is sufficiently chilled, ultrapure water is sprayed therein by the spray nozzle 3, producing frozen micro-particles 4, which are sent together with the nitrogen gas to the injection nozzle 5, by the ejector effect. The injection nozzle 5 ejects a mixture of the ice particles and the nitrogen gas against the semiconductor wafer 7 held by the arm 6. In this way, both faces of the wafer 7 are cleaned.
Since the frozen micro-particles 4 are ejected together with the nitrogen gas, a carrier gas, the jet flow which strikes the inner wall of the chamber 10 rebounds upwards. To prevent this upward rebounding a down-flow is caused by the air drawn in from the top portion of the chamber 10 which is exhausted by the exhaust blower 9 through the bottom thereof.
In such an apparatus, the cleaning chamber 10 must be rather large since the chamber 10 is designed to contain the injection nozzle 5 and the driving means 13. Also, the exhaust blower 9 is required to have a large displacement because the jet flow from the injection nozzle 5 has to be thoroughly drawn out into an exhaust duct (not shown). Therefore, the apparatus is inevitably large and has a substantial operating cost. When the displacement of the exhaust blower 9 is reduced, the jet flow is not sufficiently drawn into the exhaust duct and strikes the inner wall of the chamber 10, resulting in the upward reboundings. Dust carried in the turbulence may well land on the once-cleaned surfaces of the semiconductor wafer 7.